NL2029856B1 - Flower Cutting Device - Google Patents

Abstract

The current invention relates to an end effector device for individually picking flowers, the device comprising; — a main frame provided with connection means for connecting the end effectorto a robotic system, — a stem engaging system supported by the main frame and configured for contacting a stem portion and fixating the stem portion with respect to the stem engaging system, — a cutting system supported by the main frame and moveably arranged with respect to the stem engaging system, — a guiding system for laterally constraining the cutting system with respect to a stem [below the stem portion], and — a driving system for driving the cutting system downwards with respect to the main frame, wherein the guiding system is coupled with the cutting system to move in unity with the cutting system for laterally constraining the cutting system with respect to the stem while moving along the stem to a cutting height position.

Description

Flower Cutting Device

Field of the invention

The present invention relates to an end effector device for individually picking flowers. The device assists in the harvesting of flowers and can help to reduce the manual labour involved in the picking process. Various devices have been developed for this purpose, and these devices generally include a tool with a long arm and an end effector to perform the functions of gripping the target flower and separating the flower from a bed of plants or the like. Typically, these functions are done with one tool consisting of a vision system to determine the position of a flower, a gripper as well as a type of cutter that cuts the flower. The vision system may also determine the maturity stage of a flower in order to decide on harvestability.

Background art

Flowers are usually picked manually. When manually picking a flower like a Gerbera, the biggest challenge is to pull the flower stem into the right direction. Pulling the stem in the right direction results in a harvested flower. Pulling in the wrong direction can damage the stem of the flower or even the whole plant. This pulling in the right direction is hard to automate.

An alternative method to harvest the flower is to cut the stem. This approach has benefits from a technical point of view. The end effector does not need to make complex movements, possibly less degrees of freedom are needed and therefore the whole process can be done in less time. It is important that the stem of the flower is long enough because a flower with too short a stem has no commercial value. In practice this means that the stem when harvested needs to be as long as possible and cut to an exact length at a later stage. A Gerbera is a plant with a dense foliage. The flowers and an upper part of the stem rise above this foliage. The lower part of the stem disappears in the foliage and the origin of the stem often cannot be seen. Curves in the stem make it hard to predict the origin of the stem based on the visible part of the stem. Within the foliage there are also new flower buds which are vulnerable. The challenge is to make a cut at the right position without damaging the stem or other parts of the plant and without visual feedback of the situation within the foliage.

Summary of the invention

The present invention seeks to provide a method for operating a robotic device for individually picking flowers that is more simple with respect to movement sequence and automation and that causes less damage to the flowers.

According to the present invention, a method is provided for operating a robotic device for individually picking flowers, the device comprising a main frame supporting a stem engaging system and a cutting system; the method comprising the steps; — engaging a stem portion, and contacting the stem portion for fixating the stem portion with respect to the stem engaging system, — laterally constraining the cutting system with respect to the stem portion, — moving the cutting system downwards with respect to the main frame while following the stem, from the stem portion towards a cutting height position, and — cutting the stem at the cutting height position.

The method offers freedom to choose a first point of contact between the robotic device and the flower. It is not required to contact the stem at a cutting height position which is normally within the foliage and therefore difficult to locate using a vision system. The use of a vision system is known per se to determine a position of a flower and to decide what part of the flower to contact. It will be clear that the current invention is relevant for any flower having an elongated leafless stem or leafless pedicel that has no side branches. Another example of such a flower is Allium.

The freedom to choose a first point of contact results from a two-step approach. As a first step, the stem portion above the foliage is relatively easy to catch with a robotic arm. After the stem is caught, as a second step a cutting system is constrained with respect to the stem portion and moved downwards. This way the cutting system follows a path that is defined by the stem.

In other words; the stems above the foliage are relatively easy to catch with a robotic arm. After the stem is caught, a cutting unit is hooked up to the stem and pushed down along the length of the stem with a flexible mechanism. This way the cutting unit follows the curvature of the stem. By, as an option, measuring the pushing resistance and travelled distance of the cutting unit it can be determined if the cutting position is reached and the cut can be made.

In an embodiment, the method comprises pulling the stem portion upwards by the stem engaging system. Pulling the stem portion upwards straightens the stem and therefore, the movement of the cutting system along the stem is an even more simple movement. In addition, the stem is pretensioned to a certain degree which increases a lateral stiffness of the stem and therefore facilitates guidance of the cutting system along the stem.

In an embodiment of the method, the step of moving the cutting system downwards with respect to the main frame, and along the stem to a cutting height position comprises pushing the cutting system with respect to the main frame. Pushing the cutting system downwards facilitates movement of the cutting system through the foliage downward to the cutting height position.

In an embodiment, the method comprises engaging a stem portion above the foliage and then cutting the stem at the cutting height position within the foliage. Engaging a stem portion above the foliage is an easier task for a vision system compared to engaging the stem at a position within the foliage. This relaxes specification requirements for a vision system.

The present invention therefore provides an end effector device for individually picking flowers, the device comprising; — a main frame, — a stem engaging system supported by the main frame and configured for contacting a stem portion and fixating the stem portion with respect to the stem engaging system, — a cutting system supported by the main frame and moveably arranged with respect to the stem engaging system, — a guiding system for laterally constraining the cutting system with respect to a stem, and — a driving system for driving the cutting system downwards with respect to the main frame, wherein the guiding system is coupled with the cutting system to move in unity with the cutting system for laterally constraining the cutting system with respect to the stem while moving along the stem to a cutting height position.

The end effector device according to the invention offers freedom to choose a first point of contact between the robotic device and the flower and enables a simple movement sequence that is partly defined by the flower itself while damage to the flower is avoided. It is no longer required to contact the stem at a cutting height position which is normally within the foliage and therefore difficult to find using a vision system. To enable the simple movement, the cutting system is constrained with respect to the stem portion by a guiding system and moved downwards. The guiding system constrains the cutting system laterally with respect to the stem, in particular the stem below the stem portion. In this way the cutting system follows a path that is defined by the stem. In order for the guiding system to laterally constrain the cutting system with respect to a stem, the guiding system may partly or completely surround the stem while moving with respect to the stem. The guiding system may comprise a smooth surface facing the stem or comprises rollers or sliders or any other suitable means to make a gentle guiding contact with the stem.

In robotics, an end effector is the device at the end of a robotic arm, designed to interact with the environment, in this case the bed of flowers. The exact nature of this device depends on the application of the robot. In the strict definition, which originates from serial robotic manipulators, the end effector means the last link of the robot.

In use, the end effector is mounted to a free end of a robot arm. It will be clear that the main frame is provided with connection means for connecting the end effector to a robotic system.

In an embodiment of the end effector device, the driving system comprises an effective lateral stiffness at the guiding system that is low compared to a lateral stiffness of the stem to avoid damage to the stem. The driving system comprising a low effective lateral stiffness enables that the stem imposes a lateral position to the driving system and cutting system without building up an excessive force to the flower stem. This all the more facilitates the movement sequence of the system as well as control. The effective lateral stiffness of the driving system is a system property that can be determined by any part of the driving system like an actuator, a suspension connection between the driving system and the main frame, a connecting element between the actuator and the cutting system or any other conceivable part. In particular, the effective lateral stiffness is less than 0,5 N per cm, preferably less than 0,1 N per cm, and more preferably about 0 N per cm. This means that in practice a forced lateral movement of the guiding system with respect to the main frame of about 10 cm will cause a force of about 0 - 5 N to the stem, which is normally acceptable.

In an embodiment of the end effector device, the driving system has an effective stiffness in a driving direction, and the effective stiffness in the driving direction is greater than, in particular a number of orders of magnitude greater than, the effective lateral stiffness of the driving system at the cutting system. This enables to enter the foliage with the cutting system, while a guiding force exerted on the flower stem is still low and acceptable.

In an embodiment of the end effector device, the driving system comprises a push member for pushing the cutting system downwards with respect to the main frame. The push member facilitates to define the effective lateral stiffness of the driving system. The push member may comprise a single push element, however, any suitable number of push elements is conceivable.

For example the push member may comprises two parallel push elements that facilitates maintaining an orientation of the cutting system with respect to the stem. The push member may be an elongate member to facilitate intrusion of the foliage, however, any suitable form is conceivable. The push member may comprise a coil spring covered with a tube. This combination of a coil spring provides the right lateral stiffness, is able to enter the foliage and does not get tangled up with the flower stems.

In an embodiment of the end effector device, the push member comprises a lateral stiffness that is low compared to a lateral stiffness of the stem. The push member comprising a low effective lateral stiffness all the more enables that the stem imposes a lateral position to the guiding system.

As mentioned, the effective lateral stiffness of the driving system is a system property that can be determined by any part of the driving system. Thus the lateral stiffness of the push member co- determines the effective lateral stiffness of the driving system.

In an embodiment of the end effector device, the push member has a compressive stiffness in a longitudinal direction of the push member, and wherein the compressive stiffness is greater than, in particular a number of orders of magnitude greater than, the lateral stiffness of the push member.

In an embodiment of the end effector device, the push member comprises an alignment feature for aligning the cutting system with respect to the mainframe. Aligning the cutting system with respect to the mainframe facilitates to align the cutting system, the stem engaging system as well as the guiding system. This enables the stem engaging system to contact the stem portion and the guiding system to laterally constraining the cutting system with respect to the stem at the same time. This even more simplifies the movement sequence and control of the end effector device.

In an embodiment of the end effector device, the push member comprises a continuous 5 cavity for accommodating a power supply means operationally coupled with the cutting system for actuating the cutting system and cutting the stem. In an alternative embodiment the continuous cavity accommodates a flexible driving member operationally coupled with the cutting system for actuating the cutting system and cutting the stem. The push member comprising a continuous cavity for accommodating a power supply means and/or flexible driving member operationally coupled with the cutting system provides an integrated solution that has lower chance to become entwined in the foliage of the bed of flowers. The flexible driving member may comprise a pull cable or any other suitable element for actuating the cutting system and cutting the stem.

In an embodiment of the end effector device, the driving system comprises a driving wheel in contact with the push member. The driving wheel may comprise a friction wheel and/or a toothed wheel or any other suitable wheel member. The driving system may comprise any suitable number of wheels, like a pair of opposite wheels, or wheels, like three wheels, arranged at alternating sides or the push member to impose a curved course of the push member. It is conceivable that not all wheels are driven. Some wheels can function as a guiding wheel. The curved course of the push member causes an upper part of the push member to move away from the flower to avoid interference with the flower while a lower part of the push member can extend straight along the flower stem.

In an embodiment of the end effector device the driving system comprises a sensor system for measuring any of a pushing force and a height position of the cutting system. Measuring the pushing force and/or height position of the cutting system facilitates to determine if the cutting height position is reached and the cut can be made to provide a flower and stem with a predetermined length as desired. The pushing force may be measured based on an electric current used by a motor of the driving system. It will be clear that any other suitable force sensor is conceivable like for example a strain gauge sensor, a micro switch in combination with a spring, etc. The sensor system for measuring the height position of the cutting system may function as a relative system like by measuring a travelled distance of the cutting system with respect to the main frame. The travelled distance may be determined by a linear sensor or by an end stop switch. The sensor system for measuring the height position of the cutting system enables to cut the flower stem at a desired length. It will be clear that any other suitable system for measuring the height position of the cutting system is conceivable.

In an embodiment of the end effector device, the stem engaging system defines a catchment area open towards the stem and having a width dimension between 30 to 60 mm, in particular of about 40 mm. The width dimension of the catchment area should be big enough to facilitate catchment of a stem. The width dimension of the catchment area should be small enough to avoid interfering with other flowers/stems. The catchment area facilitates engaging and contacting the stem portion. In an alternative, the stem engaging system, cutting system as well as the guiding system co-define a common catchment area. This all the more enables the stem engaging system to contact the stem portion and the guiding system to laterally constraining the cutting system with respect to the stem at the same time.

In an embodiment of the end effector device, the stem engaging system comprises a belt member that is able to able to wrap the stem portion. The belt member provides a simple way for fixating stem portions of different diameter while still limiting a fixating force to the stem.

In an embodiment of the end effector device, the cutting system comprises a housing member defining an outer shape of the cutting system, wherein the housing member comprises an bevelled shape with respect to a direction of advancement along the stem. The bevelled shape of the housing member facilitates intruding into the foliage. The housing member may comprise a conus shape or any other suitable bevelled shape.

The invention therefore provides a robotic system comprising one or more end effectors as defined above.

Short description of drawings

The present invention will be discussed in more detail below, with reference to the attached drawings, in which fig. 1 is a schematic side view of an end effector according to the invention and a bed of flowers, fig. 2 is the end effector of fig. 1 in a different position, fig. 3 is a schematic side view of a detail of the end effector according to the invention, fig. 4 is a cross section of the detail view of fig. 3, fig. 5 is a perspective view of an example of an end effector according to the invention, and fig. 6 is a schematic side view of a robotic system comprising an end effector according to the invention.

Description of embodiments

Fig. 1 is a schematic side view of an end effector 9 according to the invention and a bed of flowers.

The end effector device 9 is configured for individually picking flowers 10.

The end effector device 98 comprises a main frame 2. The main frame 2 provides structural integrity to the end effector device 9 and supports relevant subsystems like for vision and control

(not shown) which is common for an end effector. The main frame 2 is provided with connection means 27 for connecting the end effector device 9 to a robotic system 28 (partly shown).

The end effector device 9 comprises a stem engaging system 3. The stem engaging system 3 is supported by the main frame 2. The stem engaging system 3 is configured for contacting a stem portion 5. It is important that the stem engaging system 3 fixates the stem portion 5 with respect to the stem engaging system 3. As a result, the stem portion 5 can be pulled upwards when the stem engaging system 3 and/or the end effector device 9 moves upwards. When pulling the stem portion 5 upwards, the stem 29 between the stem portion 5 and the bed 30 can be straightened and pretensioned. The stem engaging system 3 has, or in other words defines, a catchment area 22 to catch a stem portion 5. In use, the catchment area 22 is open towards the stem portion 5 in order to be able to introduce the stem portion 5 into an interior 31 of the stem engaging system 3.

The catchment area 22 may have a width dimension between 30 to 60 mm, like for example about 40 mm. The width dimension of the catchment area 22 extends transverse with respect to a stem 29. The stem engaging system 3 comprises a belt member 23. In this case, the belt member 23 fixates the stem portion 5 with respect to the stem engaging system 3. Therefore, the belt member 23 is able to wrap around the stem portion 5 to fixate the stem portion 5 in a gentle manner. The stem engaging system 3 comprises a wrapping arm 32 as shown in fig. 5 to wrap the belt member 23 around the stem portion 5.

The end effector device 9 comprises a cutting system 4. The cutting system 4 is supported by the main frame 2. The cutting system 4 is moveably arranged with respect to the stem engaging system 3. The cutting system 4 is moveable between an initial position proximate to the stem engaging system 3 as shown in this fig. 1 and proximate to a cutting position 33 as shown in fig. 2.

The cutting system 4 is configured to cut the flower stem 29 with e.g. a blade or in any other suitable manner.

The end effector device 9 comprises a guiding system 11. The guiding system 11 is configured for laterally constraining the cutting system 4 with respect to a stem 29. More precisely with respect to the stem 29 below the stem portion 5. Therefore, the guiding system 11 is coupled with the cutting system 4 to move in unity with the cutting system for laterally constraining the cutting system 4 with respect to the stem 29 while moving along the stem to a cutting height position 33.

The guiding system 11 defines a guiding system catchment area 35 to catch a stem 29 or in other words to hook up a stem 29. The guiding system 11 extends around stem accommodation 34. The guiding system 11 may entirely enclose the stem accommodation 34 in order to maintain catchment of a stem 29 within the guiding system 11 while moving along the stem. As a consequence, in case of the guiding system 11 entirely enclosing the stem accommodation 34, the guiding system 11 may comprise a closing member that is moveable between an open and closed position of the guiding system 11. It will be clear that any suitable manner to maintain the stem 29 in the stem accommodation 34 will suffice.

The end effector device 9 comprises a driving system 12. The driving system is configured for driving the cutting system 4 downwards with respect to the main frame 2. It is important to guide the cutting system 4 while minimizing a mechanical load to the stem 29. A stem 29 of a flower 10 is very vulnerable and a buckling load is easily exceeded resulting in a flower that is not saleable any more. A mechanical load like more than 5 N may already damage the stem 29. Therefore, the guiding system 11 is coupled with the cutting system 4 to move in unity with the cutting system 4.

To minimize the mechanical load to the stem 29, the driving system 12 comprises an effective lateral stiffness 13 at the cutting system 4 that is low compared to a lateral stiffness of the stem 29 to avoid damage to the stem. The effective lateral stiffness is schematically depicted as a spring 13 between the driving system 12 and the main frame 2.

Likewise, the driving system 12 has an effective stiffness 37 in a driving direction 36. The effective stiffness 37 in the driving direction is higher than the effective lateral stiffness 13 of the driving system 12 at the cutting system 4. Like for example the effective stiffness 37 in the driving direction is a one order or a number of orders of magnitude higher than the effective lateral stiffness 13 of the driving system 12 at the cutting system 4. The effective stiffness 37 in the driving direction 36 is schematically depicted as a spring 37 between the driving system 12 and the main frame 2.

The chosen wording “effective” is intended to make it clear that the effective stiffness 37 in the driving direction 36 as well as the effective lateral stiffness 13 is a system property. Such an effective stiffness results from the driving system 12 itself, the mounting of the driving system 12 to the main frame 2 or any other element that contributes to a force built up and exerted to the stem 29.

The driving system 12 comprises a push member 14. The push member 14 is configured for pushing the cutting system 4 downwards with respect to the main frame 2. The push member 14 extends between the main frame 2 and the cutting system 4. The push member 14 supports the cutting system 4. The push member 14 couples the cutting system 4 with the main frame 2. The push member 14 is arranged extendable and retractable with the driving system 12. The push member 14 is moveable along the driving direction 36.

The push member 14 comprises a lateral stiffness. The lateral stiffness of the push member is low compared to the lateral stiffness of the stem 29. It will be clear that the lateral stiffness of the push member 14 co-defines the effective lateral stiffness 13 which is a system property. The push member 14 has a compressive stiffness in a longitudinal direction 15 of the push member. The compressive stiffness of the push member is higher than the lateral stiffness of the push member.

The push member 14 is an elongate member.

The driving system 12 comprises a sensor system 21 that is schematically depicted as a functional box. The sensor system 21 is configured for measuring any of a pushing force and a height position of the cutting system 4. The pushing force is exerted by the driving system 12 to the cutting system 4.

The cutting system 4 comprises a housing member 24. The housing member 24 defines an outer shape 25 ofthe cutting system 4. The housing member 24 comprises a bevelled shape with respect to a direction of advancement 36 along the stem 29.

Fig. 2 shows the end effector 9 of fig. 1 in a different position. In a retracted position as shown in fig. 1, the cutting system 4 is proximate to the main frame 2. In other words, the cutting system 4 is docked with the main frame 2. In fig. 2, the cutting system 4 is shown in a cutting position. In the cutting position, the cutting system 4 is at the cutting height position 33. The cutting position 33 is within the foliage in this case. The stem 29 is not straight. While moving downward, the cutting system 4 has followed the stem 29. Therefore, the assembly of the cutting system 4 and the guiding system 11 are shifted a Ax with respect to the end effector 9. Thus, the end effector 9 is stationary and the assembly of the cutting system 4 and the guiding system 11 are guided by the stem 29 and shifted sideward. The force on the stem 29 is limited because of the low effective lateral stiffness 13 of the driving system 12.

The use of the end effector device is described referring to figure 1 and 2. When operating a robotic end effector device 9 for individually picking flowers 10, the method comprises the step of engaging a stem portion 5, and then contacting the stem portion 5 for fixating the stem portion 5 with respect to the stem engaging system 3. The method comprises laterally constraining the cutting system 4 with respect to the stem portion 5. After constraining the cutting system 4, the cutting system 4 moves downwards with respect to the main frame 2 while following the stem 29. The cutting system moves from the stem portion 5 towards a cutting height position 33. The cutting system 4 intrudes into the foliage 8 of the bed 30 of flowers 10. The bed 30 is grown on a layer of ground 44. Any suitable substrate will suffice. As a last step, the stem 29 is cut at a cutting height position 33.

The method may comprise pulling the stem portion 5 upwards by the stem engaging system 3. A pulling force Fou is exerted on the stem portion 5 to tension the stem 29.

The method comprises the step of moving the cutting system 4 downwards with respect to the main frame 2, and along the stem 29 to a cutting height position 33. The step may comprise pushing the cutting system 4 with respect to the main frame 2.

The method may comprise engaging a stem portion 5 above a foliage 8 and then cutting the stem at the cutting height position within the foliage 8.

Fig. 3 is a schematic side view of a detail of the end effector device 9 according to the invention. Fig. 4 is a cross section of the detail view of fig. 3. The push member 14 comprises an alignment feature 16 as shown in fig. 3. The alignment feature 16 is configured for aligning the cutting system 4 with respect to the mainframe 2. The alignment feature 16 comprises a flattened side 45 of the push member 14. In this case, the alignment feature 16 comprises two opposite flattened sides 45 of the push member 14. The alignment feature 16 aligns the cutting system 4 with respect to the mainframe 2, to facilitate that the cutting system 4 can be docked with the main frame 2 as shown in fig. 1. Course alignment of cutting system 4 with respect to the main frame 2 is done with the position of the wheels that contact the flattened sides 45. This also ensures that the push member 14 extends vertically. Fine alignment of the cutting system 4 with respect to the mainframe 2 is done by corresponding configurations of the cutting unit and the main frame 2 when the cutting system 4 is docked in the main frame 2 as shown in fig. 1.

The push member 14 comprises a lateral stiffness. In this case, the lateral stiffness of the push member 14 is defined by a flexible tube 39 as well as a coil spring 42 within the tube 39. The tube 39 is made of an engineered plastic, in this case a silicon. It will be clear that any other suitable material will suffice. The push member 14 has a compressive stiffness in a longitudinal direction 15 of the push member. The compressive stiffness is defined by the tube 39 and the spring 42 wherein the spring 42 importantly avoids buckling of the tube 39.

The push member comprises a continuous cavity 17. The cavity 17 is configured for accommodating a power supply means 18. The power supply means 18 is operationally coupled with the cutting system 4 for actuating the cutting system and cutting the stem 29.

In this case, the continuous cavity 17 accommodates a flexible driving member 19. The flexible driving member 19 is operationally coupled with the cutting system 4 for actuating the cutting system and cutting the stem 29. The flexible driving member 19 may take the form of a pull cable, a Bowden cable or the like.

The driving system 12 comprises a driving wheel 20 in contact with the push member 14. In this case, the driving system 12 comprises three driving wheels 20. The three driving wheels 20 are arranged at alternating sides 38, 39 of the push member 14. The arrangement of the three driving wheels 20 imposes a curved course of the push member 14 between the driving wheels 20. The driving system 12 may also comprise a guiding roll 41 which is not driven but only functions to guide the push member 14.

Fig. 5 is a perspective view of an example of an end effector 9 according to the invention. The cutting system 4 is shown in a position proximate to the main frame 2. The catchment area 22 of the stem engaging system 3 is aligned with the guiding system catchment area 35 defined by the guiding system 11. The guiding system 11 extends around the stem accommodation 34. The driving system 12 is configured to drive the push member 14 that is partly shown by a number of driving wheels 20. The stem engaging system 3 comprises a belt member 23. The belt member 23 fixates the stem portion 5 with respect to the stem engaging system 3. Therefore, the belt member 23 is able to wrap around the stem portion 5 to fixate the stem portion 5 in a gentle manner. The stem engaging system 3 comprises a wrapping arm 32 to wrap the belt member 23 around the stem portion 5, once a stem is caught by the catchment area 22 of the stem engaging system 3 as well as the guiding system catchment area 35 defined by the guiding system 11.

Fig. 6 is a schematic side view of a robotic system 28 comprising an end effector 9 according to the invention. The end effector 9 is schematically shown as a functional block. The robotic system is arranged along a bed 30 of flowers 10. Typically, in case of Gerbera’s, the flower is about 50-60 cm in height whereas the leaves reach to about 30-40 cm. The end effector is shown with a vision system 43. The vision system 43 is configured to determine the position of a flower, and may optionally also determine the maturity stage of a flower in order to decide on harvestability.

The present invention has been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims.

Claims (20)

Conclusions A method of operating a robot device (1) for picking flowers (10) individually, the device comprising a main frame (2) supporting a stem gripping system (3) and a cutting system (4); wherein the method comprises the steps; — engaging a handle portion (5), and making contact with the handle portion for fixing the handle portion with respect to the handle engagement system, — constraining the cutting system laterally relative to the handle portion, — moving the cutting system downwards relative to the main frame while tracking the stem (8), from the stem section to a cutting height position (7), and — cutting the stem at the cutting height position. The method of claim 1, including pulling the stem portion upwards by the stem engagement system. The method of claim 1 or 2, wherein the step of moving the cutting system downward relative to the main frame and along the stem to a cutting height position comprises pushing the cutting system relative to the main frame. A method according to any one of the preceding claims, comprising gripping a stem portion above a foliage (8) and then cutting the stem at the cutting height position within the foliage. An end effector device (9) for picking flowers (10) individually, the device comprising; — a main frame (2), — a handle gripping system (3) supported by the main frame and configured to contact a handle portion (5) and fix the handle portion with respect to the handle gripping system, — a cutting system (4) supported by the main frame and arranged movably relative to the stem engagement system, - a guide system (11) for laterally constraining the cutting system relative to a stem, and - a drive system (12) for driving the cutting system downwards relative to the main frame, wherein the guide system is coupled to the cutting system to move in unity with the cutting system for restraining the cutting system laterally relative to the stem as it moves along the stem to a cutting height position. The end effector device of claim 5, wherein the drive system includes an effective lateral stiffness (13) at the guidance system that is low compared to a lateral stiffness of the stem to prevent damage to the stem. An end effector device according to claim 6, wherein the effective lateral stiffness (13) is less than 0.5 N per cm, preferably less than 0.1 N per cm, and more preferably about 0 N per cm. An end effector device according to claim 6 or 7, wherein the drive system has an effective stiffness in a drive direction, and the effective stiffness in the drive direction is greater than, in particular several orders of magnitude greater than, the effective lateral stiffness of the drive system at the cutting system. An end effector device according to any one of the preceding claims 5-8, wherein the drive system includes a pusher (14) for pushing the cutting system downward relative to the main frame. The end effector device of claim 9, wherein the pusher has a lateral stiffness that is low compared to a lateral stiffness of the stem. An end effector device according to claim 9 or 10, wherein the pusher member has a compressive stiffness in a longitudinal direction (15) of the pusher member, and wherein the compressive stiffness is greater than, in particular several orders of magnitude greater than, the lateral stiffness of the pusher member . An end effector device according to any one of the preceding claims 9-11, wherein the pusher comprises an alignment device (18) for aligning the cutting system with respect to the main frame. An end effector device according to any one of claims 9 to 12, wherein the pusher includes a through-hole (17) for receiving a power supply means (18) operatively coupled to the cutting system for driving the cutting system and cutting the steal. The end effector device of claim 13, wherein the through cavity houses a flexible actuator (19) operatively coupled to the cutting system for driving the cutting system and cutting the stem. An end effector device according to any one of the preceding claims 5-14, wherein the drive system comprises a drive wheel (20) in contact with the pusher. An end effector device according to any one of the preceding claims 5-15, wherein the drive system comprises a sensor system (21) for measuring any of a thrust force and a height position of the cutting system. An end effector device according to any one of the preceding claims 5-16, wherein the stem engagement system defines a capture area open (22) to the stem and having a width dimension of between 30 and 60 mm, in particular of about 40 mm. An end effector device according to any of the preceding claims 5-17, wherein the stem engagement system comprises a band member (23) capable of wrapping around the stem portion. An end effector device according to any one of the preceding claims 5-18, wherein the cutting system comprises a housing member (24) defining an outer shape (25) of the cutting system, the housing member having a chamfered shape with respect to a direction of advancement (26) along the stem. 20. Robotic system comprising one or more end effectors according to one of the preceding claims 5-19.